Fuel injector with an antirebound device

ABSTRACT

A fuel injector ( 1 ) having an injection valve ( 7 ) with a movable pin ( 15 ); and an actuator ( 5 ) for moving the pin ( 15 ) between a closed position and an open position; the actuator ( 5 ) has a movable armature ( 10 ), and an antirebound device ( 20 ) interposed between the movable armature ( 10 ) and the pin ( 15 ) to connect the movable armature ( 10 ) and the pin ( 15 ) mechanically; the antirebound device ( 20 ) has a deformable elastic plate ( 32; 45; 48 ) which is annular in shape, is connected centrally to the pin ( 15 ), and is connected laterally to the armature ( 10 ) to transmit at least the closing movement of the injection valve ( 7 ) from the armature 15 ( 10 ) to the pin ( 15 ).

TECHNICAL FIELD

The present invention relates to a fuel injector.

In the following description, specific reference is made, purely by wayof example, to an electromagnetic injector for a direct fuel injectionsystem.

BACKGROUND ART

An electromagnetic fuel injector normally comprises a cylindricaltubular body having a central through hole, which acts as a fuel conduitand terminates with an injection nozzle regulated by an injection valvecontrolled by an electromagnetic actuator. More specifically, theinjection valve has a pin connected rigidly to a movable armature of theelectromagnetic actuator, and which is moved by the electromagneticactuator between a closed position, and an open position opening theinjection nozzle in opposition to a spring which keeps the pin in theclosed position.

An electromagnetic fuel injector of the type described above isillustrated, for example, in U.S. Pat. No. 6,027,050A1, which relates toa fuel injector having a movable assembly defined by a pin which, at oneend, cooperates with a valve seat, and, at the opposite end, is integralwith a movable armature of an electromagnetic actuator. The movableassembly is guided at the top by a guide cooperating with the armature,and is guided at the bottom by the end portion of the pin sliding insidea guide portion of the valve seat.

A drawback of known injectors of the type described above lies inrebound of the pin on impact with the valve seat of the injection valve,and which is not fully damped by the spring connected to the movablearmature. On the contrary, it may even produce oscillation of themovable armature, thus resulting in successive, undesiredopening/closing of the injection nozzle and, hence, undesired fuelinjection into the combustion chamber, so that the amount of fuelactually injected into the combustion chamber involves a certain randomelement.

In an attempt to eliminate rebound of the pin against the valve seat ofthe injection valve, fuel injectors have been proposed with hydraulicand mechanical antirebound devices. Known antirebound devices, however,are complex and therefore expensive to produce, and normally fail toeffectively eliminate rebound of the pin against the valve seat of theinjection valve.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a fuel injectordesigned to eliminate the aforementioned drawbacks, and which, inparticular, is cheap and easy to produce.

According to the present invention, there is provided a fuel injector asclaimed in claim 1 and, preferably, in any one of the following Claimsdepending directly or indirectly on Claim 1.

BRIEF DESCRIPTION OF THE DRAWINGS

A number of non-limiting embodiments of the present invention will bedescribed by way of example with reference to the accompanying drawings,in which:

FIG. 1 shows a schematic, partly sectioned side view of a fuel injectorin accordance with the present invention;

FIG. 2 shows a larger-scale view of the injection valve of the FIG. 1injector;

FIG. 3 shows a larger-scale view of a different embodiment of theinjection valve of the FIG. 1 injector;

FIG. 4 shows a larger-scale view of a first embodiment of a movableassembly of the FIG. 1 injector;

FIG. 5 shows a larger-scale detail of the movable assembly in FIG. 4;

FIG. 6 shows an exploded view in perspective of the movable assembly inFIG. 4;

FIG. 7 shows a larger-scale view of a second embodiment of a movableassembly of the FIG. 1 injector;

FIGS. 8 and 9 show larger-scale details of the FIG. 7 movable assemblyat two different stages in its travel;

FIG. 10 shows a larger-scale view of a third embodiment of a movableassembly of the FIG. 1 injector;

FIG. 11 shows an exploded view of the movable assembly in FIG. 10;

FIG. 12 shows a plan view of a detail of the movable assembly in FIG.10;

FIG. 13 shows a plan view of an elastic plate in FIG. 12;

FIG. 14 shows a side section along line XIV-XIV of the elastic plate inFIG. 13.

BEST MODE FOR CARRYING OUT THE INVENTION

Number 1 in FIG. 1 indicates as a whole a fuel injector which issubstantially cylindrically symmetrical about a longitudinal axis 2, andis controlled to inject fuel from an injection nozzle 3 which comes outdirectly inside a combustion chamber (not shown) of a cylinder. Injector1 comprises an actuator body 4 housing an electromagnetic actuator 5;and a valve body 6 integral with actuator body 4 and housing aninjection valve 7 activated by electromagnetic actuator 5 to regulatefuel flow through injection nozzle 3. Valve body 6 has a channel 8extending the full length of valve body 6 to feed pressurized fuel toinjection nozzle 3.

Electromagnetic actuator 5 comprises an electromagnet 9 housed in afixed position inside actuator body 4, and which, when energized, movesan armature 10 of ferromagnetic material along axis 2 from a closedposition (shown in the accompanying drawings) to an open position (notshown) opening injection valve 7 in opposition to a spring 11 whichkeeps armature 10 in the closed position closing injection valve 7. Morespecifically, electromagnet 9 comprises a coil 12 powered electricallyby an electronic control unit (not shown); and a magnetic core 13 havinga central hole to permit fuel flow to injection nozzle 3.

Armature 10 forms part of a movable assembly 14 also comprising ashutter or pin 15, which comprises a top portion integral with armature10, and a bottom portion cooperating with a valve seat 16 of injectionvalve 7 to regulate fuel flow from injection nozzle 3 in known manner.Valve seat 16 is defined in a sealing member 17 which closes the bottomof channel 8 of valve body 6 hermetically; and injection nozzle 3 isdefined in a bottom portion of sealing member 17.

Armature 10 is cylindrically annular in shape, and has a central hole 18for substantially permitting fuel flow to injection nozzle 3. A top endof spring 11 rests on a stop member 19 inside the central hole of core13, and a bottom end of spring 11 rests on movable assembly 14.

Movable assembly 14 comprises an antirebound device 20 interposedbetween armature 10 and pin 15 to connect armature 10 and pin 15mechanically, and for damping rebound of pin 15 against valve seat 16when movable assembly 14 moves from the open position to the closedposition closing injection valve 7.

As shown in FIG. 2, sealing member 17 comprises a top portion 21 havinga flared inner hole 22; and a bottom portion 23 having a cylindricalhole 24, which is an ideal continuation of flared hole 22 and comes outinside an injection chamber 25. Injection chamber 25 in turn comprises anumber of through holes 26 defining injection nozzle 3 by which fuel isinjected into the combustion chamber (not shown). Flared hole 22 andcylindrical hole 24 together define -he valve seat 16 of injection valve7.

Pin 15 terminates with a substantially spherical shutter head 27, whichrests hermetically on a surface of cylindrical hole 24 extending aboutinjection chamber 25, to prevent fuel flow to injection chamber 25 whenpin 15 is in the closed position. Four flat faces 28 (only three shownin FIG. 2) are formed parallel to axis 2 to define, with cylindricalhole 24, four passages 29 permitting fuel flow to injection chamber 25.

FIG. 3 shows an alternative embodiment of injection valve 7, in whichhead 27 has no flat faces; and four recesses 30 (only one shown fully inFIG. 3) are formed on the outer surface of sealing member 17 to definefour respective passages permitting fuel flow to four correspondingthrough holes 31 perpendicular to longitudinal axis 2 and terminatingtowards injection chamber 25. Through holes 31 are offset with respectto longitudinal axis 2 so as not to converge towards longitudinal axis2, and so as to produce swirl, in use, in the respective fuel flows. Asshown in FIG. 3, a single hole 26, sloping with respect to axis 2, ispreferably provided.

As shown in FIGS. 4 to 6, antirebound device 20 comprises an elasticcentral plate 32 welded to armature 10 and having five peripheralthrough holes 33, and a central through hole 34 for receiving pin 15. Inthis first embodiment, antirebound device 20 is complete with twoelastic lateral plates 35 and 36, which are welded to pin 15 and locatedon opposite sides of central plate 32 so as to sandwich central plate32. Lateral plate 35 has five peripheral notches 37 (or equivalentthrough holes 37) and a central through hole 38, and lateral plate 36has five peripheral through holes 39 and a central through hole 40.

As shown in FIG. 6, central hole 18 of armature 10, central hole 34 ofcentral plate 32, central hole 38 of lateral plate 35, and central hole40 of lateral plate 36 are aligned with one another and coaxial withlongitudinal axis 2 to receive pin 15; and peripheral holes 33 ofcentral plate 32, notches 37 of lateral plate 35, and peripheral holes39 of lateral plate 36 are aligned with one another to define a passagepermitting fuel flow to injection nozzle 3.

In a different embodiment not shown, as opposed to welding lateralplates 35 and 36 to pin 15, two additional bushings may be welded to pin15 on opposite sides of lateral plates 35 and 36 to grip lateral plates35 and 36 together.

The function of antirebound device 20 is to damp rebound of pin 15against valve seat 16 when movable assembly 14 moves from the openposition to the closed position closing injection valve 7, and issubstantially achieved hydraulically, i.e. by a sort of pumping effectof the fuel accumulating alternatively in two minute chambers formed onopposite sides of central plate 32 by deformation of lateral plates 35and 36 and central plate 32 itself. More specifically, when openinginjector 1 (i.e. when movable assembly 14 moves upwards in the directionof arrow F2 in FIG. 1), fuel is accumulated in and then expelled fromthe chamber formed by upward deformation (arrow F2) of lateral plate 35and central plate 32 with respect to lateral plate 36. And conversely,when closing injector 1 (i.e. when movable assembly 14 moves downwardsin the direction of arrow F1 in FIG. 1), fuel is accumulated in and thenexpelled from the chamber formed by deformation of lateral plate 36 andcentral plate 32 with respect to lateral plate 35. The pumping actionfollowed by expulsion and compression induces a certain amount of energydissipation on movable assembly 14, which is prevented from oscillating,thus preventing undesired rebound of pin 15 and undesiredopening/closing cycles of injection chamber 25.

It is important to note that, in addition to the above hydraulic effect,the antirebound function of antirebound device 20 is also achieved to asmall extent mechanically by deformation of lateral plates 35 and 36 andcentral plate 32 inducing further energy dissipation on movable assembly14.

FIGS. 7 to 9 show a different embodiment of antirebound device 20, inwhich pin 15 is hollow, and has a cylindrical inner cavity 41 coaxialwith longitudinal axis 2. The top end of pin 15 is flared, and rests ona shoulder 42 formed inside central through hole 18 of armature 10; thetop end of pin 15 is located inside hole 18 and rests on shoulder 42;and the bottom face of armature 10 comprises a recess 43 having an edge44.

An annular elastic plate 45 is welded to pin 15, and is preloadedslightly by being pushed against edge 44; an annular fuel pumpingchamber 46 is thus defined inside recess 43 by the bottom surface ofarmature 10, plate 45, edge 44 of recess 43, and pin 15; and pin 15 hasat least two openings 47 connecting cavity 41 hydraulically to channel 8of valve body 6, so that, when movable assembly 14 moves upwards in thedirection of arrow F2 (to open injection valve 7), fuel flows throughcavity 41 of pin 15 in the direction of arrows V1 and V2.

When movable assembly 14 moves in the direction of arrow F1 (to closeinjection valve 7), and once injection valve 7 is closed by the relativemovement of armature 10 and pin 15, fuel is not only expelled from thegap between edge 44 and deformable annular plate 45, but also seepsinside the narrow gap between pin 15 and hole 18 of armature 10. FIG. 8shows how the liquid fuel is subsequently fed into pumping chamber 46 byelastic plate 45 moving armature 10 back into position. In this casetoo, therefore, there is a predominant hydraulic effect, whichdissipates considerable energy to prevent movable assembly 14 reboundingagainst valve seat 16.

FIGS. 10 to 14 show a further embodiment of antirebound device 20, inwhich antirebound device 20 comprises an elastic plate 48 welded toarmature 10 and having a central through hole 49 for receiving pin 15,and three through slots 50 shaped to define a substantially annularcentral region 51 about central hole 49, and a peripheral region 52. Asshown more clearly in FIGS. 13 and 14, central region 51 of plate 48 isthinner than peripheral region 52; and, by virtue of the shape of slots50, and being thinner, central region 51 of plate 48 is highlydeformable axially (i.e. in a direction parallel to longitudinal axis 2)with respect to peripheral region 52.

As shown in FIG. 10, plate 48 is welded to armature 10 at peripheralregion 52, and is secured mechanically to pin 15, at central region 51,by two rigid annular plates 53 welded to pin 15 and located on oppositesides of plate 48 to grip plate 48 between them.

Each plate 53 has four lateral through slots 54, and a central throughhole 55. Central hole 18 of armature 10, central hole 49 of plate 48,and central holes 55 of plates 53 are aligned with one another andcoaxial with longitudinal axis 2 to receive pin 15; and slots 50 ofplate 48, and lateral slots 54 of plates 53 are at least partlysuperimposed to define a fuel passage to injection nozzle 3.

In actual use, when closing injector 1, movable assembly 14 movesdownwards in the direction of arrow F1 in FIG. 1 to bring head 27 torest against valve seat 16 with a given impact speed. Following impact,head 27 and, consequently, pin 15 remain substantially stationary, whilearmature 10 is oscillated about a final balance position by the presenceof elastic plate 48 and the kinetic energy of movable assembly 14 uponimpact. Only a minimum part of the oscillation of armature 10 istransmitted to pin 15 and head 27, and is gradually damped by thedissipation of energy in and by continual deformation of plate 48.

As will be clear from the above description, the antirebound function ofantirebound device 20 is substantially achieved mechanically, bydeformation of plate 48 inducing energy dissipation on movable assembly14; and the above mechanical effect is also accompanied to a much lesserdegree by a hydraulic effect which dissipates energy on movable assembly14 in exactly the same way as described with reference to the FIG. 4 to6 embodiment of antirebound device 20.

In a preferred embodiment shown in FIGS. 10 and 11, an annular body 56is interposed between central region 51 of plate 48 and the top plate53, to enable accelerated pretravel of armature 10 when opening injector1 (i.e. when movable assembly 14 moves upwards in the direction of arrowF2 in FIG. 1). At the start of the opening stage, head 27 contacts valveseat 16. As of this condition, armature 10 is drawn electromagneticallytowards electromagnet 9, in opposition to the force exerted by spring11, so that, to open injection valve 7, armature 10, and with it thewhole of movable assembly 14, must accelerate from a rest condition tomove upwards in the direction of arrow F2 in FIG. 1. Annular body 56 isprovided so that the initial travel of armature 10 takes place withoutinvolving pin 15 for a distance defined by the thickness of annular body56. In other words, initially, for a distance substantially equal to thethickness of annular body 56, armature 10 moves upwards without movingpin 15, on account of elastic plate 48 not initially contacting rigidtop plate 53. Only after armature 10 has travelled a distance defined bythe thickness of annular body 56, does elastic plate 48 contact rigidtop plate 53, and armature 10 continues moving upwards together with pin15.

The accelerated pretravel function of annular body 56 is to assistinitial acceleration of armature 10, during which armature 10 mustovercome a small amount of inertia (pin 15 does not move). This improvesthe dynamic performance of injector 1 when it is opened, in that one ofthe problems of electromagnetic fuel injectors is the sluggish openingresponse caused by poor initial acceleration of the magnetic armature.

As shown in FIG. 1, an adapter 59 is provided between a feed pipe 57,for feeding fuel to injector 1, and a head 58 of injector 1, andcomprises a cylindrical main body 60 having a central through hole 61coaxial with longitudinal axis 2; and each end of main body 60 has anannular recess 62 housing a sealing ring (O-ring) 63 and anantiextrusion ring 64.

It is important to note the innovative “male/male” design of adapter 59,in that both feed pipe 57 and head 58 of injector 1 have “female” ends,as shown in FIG. 1. Using adapter 59 ensures fluidtight sealing of theconnection between feed pipe 57 and head 58 of injector 1, even in theevent of misalignment of head 58 of injector 1 with respect to feed pipe57. That is, adapter 59 provides for correcting any relative positionerrors (due to manufacturing and assembly tolerances) between feed pipe57 and head 58 of injector 1.

As will be clear from the foregoing description, armature 10 also actsas a top guide for pin 15, i.e. assists in keeping pin 15 aligned withrespect to valve seat 16, and allows pin 15 to move along axis 2 underthe control of electromagnetic actuator 5.

The particular design of shutter head 27 permits a sliding connection ofhead 27 and cylindrical hole 24, so that pin 15, and consequentlymovable assembly 14, is guided at the bottom by the connection betweenhead 27 and sealing member 17, and is guided at the top by theconnection between armature 10 and the inner walls of channel 8 of valvebody 6. Converting the bottom guide of movable assembly 14 from acylindrical to a spherical-cylindrical connection, together with theparticular connection of armature 10 and pin 15 by antirebound device20, provides for correcting any misalignment (due to manufacturingand/or assembly tolerances), thus enabling use of a one-piece drawnvalve body 6 requiring no further grinding inside.

1-14. (canceled)
 15. A fuel injector (1) comprising an injection nozzle(3); an injection valve (7) having a movable pin (15) for regulatingfuel flow through the injection nozzle (3); and an actuator (5) formoving the pin (15) between a closed position and an open positionopening the injection (7) in opposition to a spring (11) which keeps thepin (15) in the closed position; the actuator (5) comprising a movablearmature (10) connected mechanically to the pin (15), and an antirebounddevice (20), which (20) is interposed between the movable armature (10)and the pin (15) to at least partly connect the movable armature (10)and the pin (15) mechanically and comprises at least one deformableelastic plate (32; 45; 48) which is annular in shape, is connectedcentrally to the pin (15), and is connected laterally to the armature(10) to transmit at least the closing movement of the injection valve(7) from the armature (10) to the pin (15); the injector (1) ischaracterized in that the deformable elastic plate (32; 48) is rigidlysecured centrally to the pin (15), and is rigidly secured laterally tothe armature (10); the antirebound device (20) comprising two annularfirst bodies (35, 36; 53) connected rigidly to the pin (15) to grip theelastic plate (32; 48) between them.
 16. An injector (1) as claimed inclaim 1, wherein the deformable elastic plate (32; 48) is weldedlaterally to the armature (10).
 17. An injector (1) as claimed in claim1, wherein the elastic plate (32; 48) and the annular first bodies (35,36; 53) comprise respective through holes (33, 37, 38; 50, 54)permitting fuel passage.
 18. An injector (1) as claimed in claim 1,wherein the annular first bodies (35, 36) are elastic and deformable.19. An injector (1) as claimed in claim 1, wherein the annular firstbodies (53) are rigid and substantially undeformable.
 20. An injector(1) as claimed in claim 5, wherein a second annular body (56) isinterposed between a top annular first body (53) and the elastic plate(48) to define an accelerated pretravel of the movable armature (10) atthe opening stage.
 21. An injector (1) as claimed in claim 5, whereinthe elastic plate (48) has a through central hole (49) for receiving thepin (15), and a number of through slots (50) shaped to define asubstantially annular central region (51) about the central hole (49),and a peripheral region (52); the central region (51) of the elasticplate (48) being highly deformable axially with respect to theperipheral region (52).
 22. An injector (1) as claimed in claim 7,wherein the central region (51) of the elastic plate (48) is thinnerthan the peripheral region (52).
 23. An injector (1) as claimed in claim1, wherein the pin (15) is hollow, and has a flared top end to rest on ashoulder (42) formed in a through central hole (18) of the armature(10); the top end of the pin (15) being located inside the hole (18) andresting on the shoulder (42); the bottom face of the armature (10)having a recess (43) which has an annular edge (44) and is closed by theannular elastic plate (45) to define a pumping chamber (46); and the pin(15) having a number of through openings (47) permitting fuel flowthrough the pin (15) to the injection nozzle (3).
 24. An injector (1) asclaimed in claim 9, wherein the annular elastic plate (45) is welded tothe pin (15), and is pushed against the edge (44) of the recess (43) toimpart a slight preload to the elastic plate (45).
 25. An injector asclaimed in claim 1, wherein the actuator (5) is an electromagneticactuator, and comprises a fixed core (13) connected to a coil (12) andwhich attracts the movable armature (10) magnetically in opposition tothe force of the spring (11).
 26. An injector as claimed in claim 1,wherein the pin (15) has a substantially spherical shutter head (27)which engages a valve seat (16) of the injection valve (7).
 27. Aninjector as claimed in claim 12, wherein the shutter head (27) comprisesa number of flat faces (28) defining, with at least one portion of thevalve seat (16), a number of passages (29) permitting liquid fuel flowto an injection chamber (25) of the injection nozzle (3).
 28. Aninjector as claimed in claim 12, wherein the shutter head (27) rests onan inlet portion of an injection chamber (25) of the injection nozzle(3); the injection chamber (25) being supplied by transverse holes (31)arranged so as not to converge towards a longitudinal axis (2) of theinjector (1), and so as to impart swirl to the fuel flow.